Posted by Damir [ 213.202.68.64 ] on December 23, 2004 at 09:41:31:
In Reply to: Re: My idea... posted by Wayne Parham on December 22, 2004 at 16:11:50:
Thank you for your confidence. It`s no problem - when we have a driver, SET power amp is just a few resistors, capacitors, OPTs, output tubes+sockets. But - if we use about 300V B+, then we have a few choices for the output tube. One of the simpler solutions would be EL34, triode connected.
Pro`s - IDHT with "standard" 6,3V heater, easy to drive (say 16Vrms max, then our line-stage can "drive" it with 1Vrms input, +"reserve" 6dB with 2Vrms CD output). Bias is easy - just one resistor + capacitor (cathode bias).
Con`s - With Uak about 280V, and Ugk =20...24V, and OPTs with Za=2,5k-5k, we can expect only about 2-3,5W output. Sensitive speakers is a must...
Another candidate could be 2A3, "classic" OP (Uak=250V, Ugk=-45V, Ia=60mA, Za=2k5, Pout=3,5W). "Cool" DHT, but now we have some complications - we need 2,5V filament winding, filament hum balancing pot, and the most important - 2A3 "needs" 45Vp=90Vpp=32Vrms input AC voltage for max. power. Our 5687 linestage has A~17 and this is just enough, but with no "reserve" - it`s desirable to have at least 3dB more amplification, for "quiet" CDs. We can (almost) get it if we use similar ECC99 tube (mu=22).
Well, I`d like to see some discusion (if anybody is interested) - what to do - separate linestage and power amp, or no. Then - which tube to use, topology, etc.
I can post a schematics, calculate the component values, give descriptions and some building guidance, etc.
Where to find the parts - I`d like to see a discussion, too.
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